Progress in FY2011 was in the following areas: 1. DETERMINATION OF BETA-SHEET STRUCTURES IN YEAST PRIONS. We performed new experiments on full-length Ure2p yeast prion fibrils, showing conclusively that the fibril core is formed by the N-terminal, Asn- and Gln-rich domain and that the beta-sheet structure in the core is parallel and in-register. These results, based on solid state NMR of protease-treated fibrils, disprove an interpretation of solid state NMR data from a Swiss group, in which they claimed that the C-terminal globular domain of Ure2p is involved in the fibril core. 2. INVESTIGATIONS OF FUNCTIONAL AMYLOIDS. We have completed solid state NMR studies of Pmel17 fibrils, reported to facilitate melanin polymerization within mammalian melanosomes. The NMR data show that only about 30% of the Pmel17 repeat-domain sequence participates in the Pmel17 fibril core, and that the core structure is highly polymorphic. 3. MAMMALIAN PRION PROTEIN FIBRILS. Solid state NMR measurements on fibrils formed by recombinant mammalian PrP (full-length, Syrian hamster sequence) show that these fibrils contain parallel beta-sheets, and that the fibril core is formed primarily by a 30-residue segment near the C-terminus (collaboration with I.V. Baskakov). Although these fibrils are not infectious as prions, they may resemble infectious PrP aggregates in many respects.